124 research outputs found
Combining chemical and X-Ray microtomography investigations on crustal xenoliths at Mount Etna: evidence of volcanic gas fluxing
No full textCrustal xenoliths embedded in lavas offer chances to provide information on the lithology of the volcano basement and the process occurring during magma ascent. In this work we studied seven xenoliths found among the scoriae ejected during several paroxysms occurred between 2011 and 2016 at the South East Crater (SEC) of Mount Etna volcano. These samples are characterized by massive presence of glass and vesicles resulting in a foam-like appearance of their texture. A detailed study of their textural and chemical features was carried out combining XRF, SEM-EDS, two-dimensional observation and Synchrotron X-ray microtomography (3D imaging). This multidisciplinary approach allowed us to identify and quantify the components of the samples, individuate the likely provenance rock, ascribable to the Numidian Flysch outcropping west of the Etnean edifice. 2D and 3D imaging were successfully applied to estimate the amount of the phases constituting the samples (grains + glass + vesicles) and the degree of partial melting that occurred during the interaction with the basaltic melt and gaseous phase. The sedimentary rocks underwent profound changes led by partial melting, gas fluxing, vesiculation and selective alkali enrichment. These processes could not be driven exclusively by the prolonged contact with the molten phase but must be considered as result of a significant contribution from the volatiles rising through the plumbing system and the sedimentary basement
Morphological Evolution of Zn-Sponge Electrodes Monitored by In Situ X-ray Computed Microtomography
No full textUse of Zn sponges has been recently proposed as an effective means of limiting the shape change and dendrite formation issues, affecting the anodes of electrically rechargeable Zn-based batteries. This paper contributes to this field of research with in situ X-ray computed microtomography (XCMT) monitoring of the morphological and chemical changes undergone by Zn-sponge anodes during electrochemical cycling. Starting from a pristine anode, fabricated in the discharged state, this was first charged and then subjected to a representative series of charge-discharge sequences and, in correspondence, it was studied by XCMT in order to determine (i) the volume fractions of Zn and ZnO, porosity, and their space arrangement and (ii) the degree of connectivity of the elemental Zn framework. Good stability of the metal framework, reversibility of the Zn and ZnO phases, and their space distribution, with a limited alteration of the pore structure, were observed over more than 60 charge-discharge cycles
Quantitative Analysis of Pore-Network and Permeability Estimation in Deformed Porous Carbonate Grainstones
No full textThis study investigates the pore-network properties and the permeability of deformed porous carbonate grainstones located in Northwestern Sicily and Abruzzo region, Italy. Even though the studied grainstones present similar values of porosity, their permeability varies between three to four orders of magnitude. In order to explain this permeability difference, we performed a three-dimensional quantitative analysis of the pore-network including porosity, pore connectivity and specific surface area. For assessing those properties, samples of deformed carbonate grainstones were scanned implementing X-ray computed microtomography techniques. In addition, permeability was computed by means of Lattice-Boltzmann simulation. The effect of each pore-network property (porosity, specific surface area, pore connectivity) on permeability was evaluated by means of scatter plots considering both host rocks and deformation bands.
In the highly porous host rock, the permeability is mainly controlled by the specific surface area, which is linked to both grain size and roughness. Within deformation bands, permeability reduction is related to low pore-network connectivity caused by compaction and cementation
Deciphering lava flow post-eruption differentiation processes by means of geochemical and isotopic variations: A case study from Mt. Etna volcano
No full textWe report results from geochemical and isotopic analyses conducted on nine samples collected from the vertical
section of a pahoehoe lava flow unit from Mt. Etna volcano. Textural observations in the field show that,
during lava emplacement, volatile exsolution and degassing allowed the nucleation and growth of bubbles,
which subsequently rose from the base towards the uppermost lava crust. The amount of phenocrysts is
low (about 12 vol.%) and their compositions are comparable to intratelluric crystals analyzed for from historical
and recent products. In contrast, from the basal zone to the uppermost lava crust, groundmass microlites
are characterized by progressively more primitive compositions, i.e., olivines and clinopyroxenes show increasing
Mg#, plagioclases are enriched in anorthite, and the ulvospinel content in titanomagnetites increases.
Calculations based on thermodynamic models, thermometers and oxygen barometers indicate
that, during post-eruption conditions, crystals formed at higher crystallization temperatures with increasing
vertical height. The redox state of the melt progressively increased from the base towards the uppermost
crust of the lava flow as is attested by increasing Fe2O3/FeO ratios in clinopyroxene and titanomagnetite.
The lowest fO2 is recorded at the basal zone and suggests that this part of the lava was inaccessible to diffusion
of atmospheric oxygen at the time of emplacement; whereas, the highest fO2 measured for the uppermost
lava crust testifies to post-eruptive hydrogen loss, mainly transported by carrier gas phases.
Whole-rock analyses of lava samples also indicate higher Fe2O3/FeO ratios with increasing vertical height
as well as substantial enrichments in MgO and transitional elements. Results from both mass balance and
Rayleigh fractionation calculations show that about 6 vol.% of titanomagnetite and olivine microlites accumulated
in the upper parts of the lava flow during emplacement. At the same time, due to progressive volatile
exsolution, concentrations of Cl, F and Cs in whole rock decreased from the base towards the uppermost
lava crust; indeed, oxygen isotopes indicate a substantial 22 wt.% of CO2 degassing. From this, we conclude
that even short-term exposure to post-eruptive conditions results in significant local compositional changes
for lava flows at Mt. Etna volcano.Published115-1272R. Laboratori sperimentali e analiticiJCR Journalrestricte
Solidification and turbulence (non-laminar) during magma ascent. Insights from 2D and 3D analyses of bubbles and minerals in an Etnean dyke
No full textSolidification, emplacement and fluid dynamics of a sub-volcanic rock at Mt Etna have been investigated through two-dimensional (2D) and three-dimensional (3D) textural analyses of the hosted bubbles and minerals. This rock is a 4 center dot 3 m thick aphyric dyke (DK) that solidified at a depth of 100-300 m, below the pristine surface level. Seven samples from the dyke rim (DK1) to core (DK7) have been analysed in two dimensions by using a high-resolution scanner, a transmission optical microscope and scanning electron microscopy imaging with back-scattered electrons, and in three dimensions by microfocus X-ray computed tomography. Field observations and mesoscopic polished rock surfaces show bubble-rich, -poor and -free patches even in rock pieces of a few cubic centimetres, with changes in sizes and shapes; even so, their shapes and spatial arrangement can never be attributed to high degrees of strain. In parallel, the amount of bubbles irregularly varies from dyke rim to core, whereas plagioclase (plg), clinopyroxene (cpx), titanomagnetite (timt), and olivine (ol) show only limited variations. The fabric of bubbles retrieved by 3D orientation of their maximum length (i.e. elongation) is invariably random in space for each DK sample. These bubble features have been attributed to transitional to turbulent flows; that is, non-laminar regimes (Reynolds number > 1000), predicted for a long time from numerical models and that occurred before the crystallization of minerals. Water solubility, volume of bubbles, magma density and viscosity models indicate that, at pressure higher than 10 MPa, 1 wt % H2O was dissolved in the original trachybasaltic magma, which, in turn, was close to its liquidus temperature. As the pressure decreased at very shallow levels, the magma significantly degassed and volatile exsolution induced marked crystallization (mostly plg followed by cpx). The viscosity of the system increased, decelerating and halting the magmatic suspension. The textures and fabrics of bubbles were suddenly frozen in, despite crystals continuing to grow under the effect of cooling rate variables from the inner (DK7) to outer (DK1) dyke portions. Fluid-dynamic computations suggest that the DK trachybasaltic magma ascended with a velocity of few metres per second in a transitional to turbulent regime, before the growth of minerals
The Skaros effusive sequence at Santorini (Greece): Petrological and geochemical constraints on an interplinian cycle
No full textSantorini volcanic complex (Greece) is the result of a long evolutionary history, marked by the alternation of explosive (Plinian) eruptions and interplinian low explosive/effusive eruptive cycles. Products emitted during the interplinian stages are well exposed along the rim of the calderic structure formed during the major Minoan (3.6 ka) Plinian eruption. We conducted a systematic sampling of the basaltic to dacitic lavas erupted by the interplinian volcanic centre of Skaros, active between 67 and 54 ka. The continuously exposed products of the Skaros lifecycle offer the tremendous opportunity to reconstruct the petrological evolution of the volcanic centre, and in turn to provide new insights on the behaviour of Santorini feeding system during interplinian stages. The combination of whole-rock, mineral chemistry and synchrotron X-ray computed microtomography analyses enabled us to decipher the main physico-chemical parameters of the Skaros plumbing system that drove ascent and differentiation processes of magmas. Results indicate that the main magma ponding zone beneath Skaros centre extended from 12 to 4 km b.s.l., where it underwent frequent refilling by basaltic melts. In the later evolutionary stage of the Skaros system, the basaltic replenishment became less frequent allowing the ultimate differentiation of magma towards dacitic composition. The shallow nature of the magma ponding zone, sited well above the H2O saturation depth, favoured the continuous degassing and inhibited the increase of vapor pressure during differentiation, preventing the onset of explosive eruptions, as in case of the major explosive events at Santorini
Thermal and morphological investigations of alkali activated materials based on Sicilian volcanic precursors (Italy)
No full textInsights on thermal behavior and microstructures of AAMs based on Sicilian volcanic precursors (i.e.,
volcanic ash, "ghiara" and pumice) have been performed. A multidisciplinary approach by means of
thermogravimetric analysis coupled to Fourier Transform Infrared Spectroscopy and X-ray Computed
Microtomography has been used with the aim to define the influence of reactants involved in the process.
The obtained results show: i) the increase of metakaolin shifts the gas emission toward lower
temperatures; ii) the positive relation between mass loss and liquid/solid ratio; iii) the influence of particle
size of precursors on the pore development
Unraveling the solidification path of a pahoehoe "cicirara" lava from Mount Etna volcano
No full textThe solidified surface of a lava flow reflects the
viscosity of its molten fraction and the crystal content during
flow; crystal-poor basaltic lavas produce pahoehoe fields,
whereas crystal-rich ones solidify with aa carapaces. At
Mount Etna, volcano aa morphologies are very common,
whereas pahoehoe lavas are rare. The latter are locally
named “cicirara” due to the presence of centimeter-sized
plagioclase phenocrysts much more abundant than in aa
lavas. The phenocryst content of “cicirara” lavas contrasts
with the low viscosity generally associated with pahoehoe
morphology. Therefore, to reconcile the discrepancy between
textural and volcanic observations, we have studied
the most primitive pahoehoe “cicirara” lava sampled until
now. Two samples at 0.5 and 1 m from the bottom of the 2-
m thick lava flow were investigated on the basis of their
mineral compositional variations and textural features, i.e.,
size frequency and crystal size distribution (CSD). Results
coupled with rheological models indicate that only large
phenocrysts of plagioclase (>1 mm) and clinopyroxene have
grown before eruption. Thermobarometric models and petrological
computations based on the composition of plagioclase
and clinopyroxene phenocryst cores highlight that
only a small amount (10–15 vol.%) of crystals equilibrated
at 12 km of depth. Cumulative size frequency and CSD data
also indicate that plagioclase and clinopyroxene phenocryst
rims grew heterogeneously and coalesced around their cores
at depths <1 km, before eruption. In this view, the “cicirara”
lava was erupted with a low crystalline content that favoured
the formation of its pahoehoe surface; however, crystals
with a size <1 mm (~75 vol.%) solidified at post-eruptive
conditions. Our findings underline that the emplacement of
high-viscosity aa or low-viscosity pahoehoe lavas is driven
by the degree of undercooling imposed by the volatile
exsolution rate in the shallowest portion of the Etnean
plumbing system. A slow magma ascent rate promotes
significant intratelluric degassing and widespread nucleation;
consequently, the viscosity of the suspension significantly
increases leading to an aa morphology. In contrast,
pahoehoe “cicirara” lavas are associated with a rapid rise to
the surface of poorly degassed, undercooled magmas.Published7032R. Laboratori sperimentali e analiticiJCR Journalrestricte
PyPore3D: An Open Source Software Tool for Imaging Data Processing and Analysis of Porous and Multiphase Media
No full textIn this work, we propose the software library PyPore3D, an open source solution for data processing of large 3D/4D tomographic data sets. PyPore3D is based on the Pore3D core library, developed thanks to the collaboration between Elettra Sincrotrone (Trieste) and the University of Trieste (Italy). The Pore3D core library is built with a distinction between the User Interface and the backend filtering, segmentation, morphological processing, skeletonisation and analysis functions. The current Pore3D version relies on the closed source IDL framework to call the backend functions and enables simple scripting procedures for streamlined data processing. PyPore3D addresses this limitation by proposing a full open source solution which provides Python wrappers to the the Pore3D C library functions. The PyPore3D library allows the users to fully use the Pore3D Core Library as an open source solution under Python and Jupyter Notebooks PyPore3D is both getting rid of all the intrinsic limitations of licensed platforms (e.g., closed source and export restrictions) and adding, when needed, the flexibility of being able to integrate scientific libraries available for Python (SciPy, TensorFlow, etc.)
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